1. Field of the Invention
An object of the present invention is a method to record images or pictures by laser as well as means to implement it.
In the present description, the term "picture" refers to graphic representations as well as to printed text and photographs, etc.
In certain applications, a picture has to be formed on a medium which is hard to falsify or counterfeit.
2. Description of the Prior Art
Various methods are known for this purpose. Among them, we might cite the printing of blank bills where a chemical transfer process is used. Various special devices are used to make this method hard to falsify but, for certain uses, the method does not make it difficult enough to counterfeit.
Other methods, such as those used to manufacture digital optical disks, use a mechanism for the ablation of a layer selected to absorb incident radiation. Once the absorbent layer is removed by radiation, it lets the medium appear at specific places, thus forming an picture. These methods, however, do not give good "rendering", namely quality (picture definition, contrast, etc.) similar to that of pictures made by printing.
An object of the present invention is therefore, the making of a picture with rendering quality comparable to that of a printed picture which is as difficult as possible to falsify and as difficult as possible to counterfeit, a method of this type being applied notably in the making of top security documents such as identity papers for example.